Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a nacelle mounted on the tower, a generator positioned in the nacelle, and a rotor having one or more rotor blades coupled to a hub. The rotor blades convert kinetic energy of wind into mechanical energy using known airfoil principles. A drivetrain transmits the mechanical energy from the rotor blades to the generator. The generator then converts the mechanical energy to electrical energy that may be supplied to a utility grid.
The rotor blades may be rotatably coupled to the hub. In this respect, pitch adjustment mechanisms may rotate the rotor blades relative to the hub to adjust a pitch angle of the rotor blades. For example, the pitch adjustment mechanisms may adjust the pitch angle of the rotor blades during a start-up sequence of the wind turbine. However, when the rotor blades fall below a minimum pitch angle during the start-up sequence, the rotor blades may experience negative stall.
Conventional systems and methods for controlling the pitch angle of the rotor blades during the start-up sequence of the wind turbine may require multiple start-up sequence attempts before the wind turbine is able to generate power. More specifically, conventional systems and methods may initiate a start-up sequence when the wind turbine experiences a wind speed sufficient to power the generator. Once the start-up sequence is initiated, the pitch adjustment mechanisms may adjust the pitch angle of the rotor blades at a predetermined rate. However, the wind speed experienced by the rotor blades may change during the start-up sequence. A change in wind speed may, for example, cause the rotor blades fall below the minimum pitch angle and experience negative stall. When negative stall occurs, the systems and methods must stop and reinitiate the start-up sequence of the wind turbine. In certain instances, this may occur multiple times before the wind turbine is able to produce power. In this respect, multiple start-up sequence attempts may cause significant wear to the pitch adjustment mechanisms and other wind turbine components.
Accordingly, improved wind turbines, and, in particular, improved systems and methods for controlling the pitch angle of wind turbine rotor blades, are desired in the art. Specifically, systems and methods that do not require multiple start-up attempts and produce relatively less wear on the wind turbine would be advantageous.